A heart is the center of a person's circulatory system. It includes a complex electro-mechanical system performing two major pumping functions. The left portions of the heart, including the left atrium and the left ventricle, draw oxygenated blood from the lungs and pump it to the organs of the body to provide the organs with their metabolic needs for oxygen. The right portions of the heart, including the right atrium and the right ventricle, draw deoxygenated blood from the body organs and pump it to the lungs where the blood gets oxygenated. These pumping functions are accomplished by contractions of the myocardium, i.e., heart muscles. In a normal heart, the sinoatrial (SA) node, the heart's natural pacemaker, generates electrical impulses, called action potentials, that propagate through an electrical conduction system to various regions of the heart to excite the muscular tissue of these regions. Coordinated delays in the propagations of the action potentials in a normal electrical conduction system cause the various portions of the heart to contract in synchrony to result in efficient pumping functions. A blocked or otherwise abnormal electrical conduction and/or a deteriorated myocardium cause asynchronous contraction of the heart, and result in poor hemodynamic performance including diminished blood supply to the body.
Implantable pacemakers have been used to treat patients suffering from, for example, an abnormal SA node, a dysfunctional electrical conduction system, and/or a deteriorated myocardium. A pacemaker generates electrical pulses that substitute for the action potentials to excite the myocardium. The electrical pulses are delivered to one or more sites in or about the heart through one or more pacing leads with electrodes, bypassing at least a portion of the natural electrical conduction system. The effectiveness of a pacing therapy using an implantable pacemaker in improving a patient's hemodynamic performance depends on the patient's particular cardiac and other physical conditions.
To predict whether a patient will benefit from a pacing therapy delivered by an implantable pacemaker, the patient's physiological and/or pathological conditions are evaluated. The evaluation becomes difficult when the patient's abnormal conditions, or symptoms, occur occasionally or intermittently. For example, for a patient suffering from recurrent fainting, it often occurs that when the patient sees a physician, the symptoms are not present, and the physician is unable to determine what caused the fainting. A solution is to use an implantable cardiac monitor that records the patient's electrocardiogram during detected episodes of abnormal conditions. The recorded electrocardiogram provides the physician with information needed to determine the cause of the symptoms and to predict whether the patient will likely benefit from the pacing therapy.
One problem is, however, that if the patient is indicated for cardiac pacing therapy, the implantable cardiac monitor needs to be explanted, and an implantable pacemaker needs to be implanted. That is, two separate implantable medical devices are needed, imposing a high cost upon the patient or another responsible party, such as an insurer or a hospital.